In the production of silicon crystals grown by either the Czochralski (Cz) method or the continuous Czochralski (CCZ) method, polycrystalline silicon is first melted within a crucible, such as a quartz crucible, of a crystal pulling device to form a silicon melt. The puller then lowers a seed crystal into the melt and slowly raises the seed crystal out of the melt. As the seed crystal is grown from the melt, solid polysilicon is added to the melt to replenish the polysilicon that is incorporated into the growing crystal. The addition of polysilicon to the melt reduces the temperature of the melt where the solid polysilicon is added. As a result, additional heat is needed to melt the solid polysilicon, and maintain the melt in a liquid state.
Known crystal pulling devices use external heaters to conductively heat the melt through the crucible. Known crucibles are typically opaque and have a relatively low thermal conductivity. As such, the crucible must be heated to a relatively high temperature to maintain the melt in a substantially liquid state. However, at such high temperatures, carbon from the graphite susceptor, which supports the crucible, and the silica from the quartz crucible react with each other. This reaction generates oxidized carbon and silicon products in gaseous form. The gases get carried away by the flowing inert gases within the puller system and deposited into the silicon melt, thus contaminating the melt with carbon. Silicon crystals grown from this melt, then, have a high carbon content and may potentially lead to silicon wafers that are out of specification. Furthermore, because the gaseous reaction products are being carried away by the inert gases in the crystal puller, the exterior surfaces of the growing ingot are exposed to the gaseous reaction products and may react further. This leads to continuous contamination of the silicon melt.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.